Treading exerciser



FIG. 1 is a perspective view of a treading exerciser showing my design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left side elevational view thereof; and,

FIG. 4 is a top plan view thereof.

The broken lines portions of FIGS. 2, 3 and 5 form no part of the claimed design. 

The ornamental design for a treading exerciser, as shown and described. 